Desulphurizing plant alloy

ABSTRACT

DIRECTED TO ALLOYS HAVING IMPROVED RESISTANCE TO CARBURIZATION AND SULFIDATION, GOOD STRESS RUPTURE STRENGTH, AND STRUCTURAL STABILITY ON PROLONGED HEATING CONTAINING, BY WEIGHT, ABOUT 32% TO ABOUT 48% NICKEL, ABOUT 19% TO ABOUT 24% CHROMIUM, ABOUT 2.2% TO ABOUT 3.5% ALUMINUM, AND THE BALANCE ESSENTIALLY IRON, WHEREIN THE NICKEL CONTENT AND THE CHROMIUM CONTENT ARE CORRELATED TO THE ALUMINUM CONTENT SUCH THAT THE MINIMUM NICKEL CONTENT INCREASES AND/OR THE MAXIMUM CHROMIUM CONTENT DECREASES AS THE ALUMINUM CONTENT INCREASES.

p 2. 1012 P. 1. FONTAINE 3,690,873

DESULPHURIZING PLANT ALLOY Filed July 9, 1969 f 0 x x 1 I9 20 (Z 22 23 24 PAUL JSIDORE FONTAINE In oenlor Altorne y United States Patent Ofice 3,690,873 DESULPHURIZING PLANT ALLOY Paul Isidore Fontaine, Solihull, England, assignor to The International Nickel Company, Inc., New York, N.Y. Filed July 9, 1969, Ser. No. 840,242 Claims priority, application Great Britain, July 9, 1968, 32,650/68 Int. Cl. C22c 19/00, 39/20 US. Cl. 75-134 F ABSTRACT OF THE DISCLOSURE Directed to alloys having improved resistance to carburization and sulfidation, good stress rupture strength, and structural stability on prolonged heating containing, by weight, about 32% to about 48% nickel, about 19% to about 24% chromium, about 2.2% to'about 3.5% aluminum, and the balance essentially iron, wherein the nickel content and the chromium content are correlated to the aluminum content such that the minimum nickel content increases and/or the maximum chromium content decreases as the aluminum content increases.

Hot gas mixtures containing hydrogen sulfide and hydrogen, which are frequently encountered in petroleum refining processes, are highly corrosive to both nickel-base and iron-base alloys, and there is a need for an inexpensive alloy that has a good resistance to corrosion both by these gas mixtures and in oxidizing and carburizing environments, and also has good high-temperature strength.

It is well known that the addition of aluminum to steels and nickel-base alloys improves their resistance to hightemperature oxidation and sulfidation, and aluminum-containing nickel-chromium-iron alloys with 33% nickel and 21% chromium have been found to be particularly resistant to corrosion by hydrogen sulfide/hydrogen atmospheres in the temperature range 400 C. to 800 C. The properties of these alloys have been investigated by J. J. Moran and J. W. Schultz, who reported in the Proceedings of the 7th World Petroleum Congress, 1967, 6, 201- 208, that their corrosion-resistance increases with increasing aluminum content and is greatest with from 2% to 4% aluminum.

The presence of these amounts of aluminum, however, renders the 33% nickel-21% chromium-iron alloys susceptible on prolonged heating to structural changes which cause embrittlement and loss of impact strength. Their usefulness for any purposes is thus greatly reduced. The alloys can be stabilized to some extent by heating in the temperature range 925 C. to 1040 C. before putting them into service, but this is not entirelysatisfactory.

The present invention is based on the discovery that an improved combination of corrosion resistance, stress-rupture strength and structural stability on prolonged heating results if the nickel, chromium and aluminum contents are correlated in a special manner.

It is an object of the invention to provide a nickelchromium-iron-aluminum alloy having a specially correlated composition to confer a special combination of properties, including resistance to sulfidation and carburization, elevated temperature strength and structural stability on prolonged heating.

It is a further object of the invention to provide an alloy of specially correlated com-position characterized by resistance to embrittlement as indicated by substantial retention of impact properties upon prolonged heating.

Other objects and advantages of the invention will become apparent from the following description taken in 8 Claims Patented Sept. 12, 1972 conjunction with the accompanying drawing characterizing alloys in accordance with the invention.

Alloys according to the invention contain, by weight, from 0.02% to 0.15% carbon, from 32% to 48% nickel, from 19% to 24% chromium, and from 2.2% to 3.5% aluminum. T

As the aluminum content is increased, the minimum content of nickel required to ensure freedom from embrittlement on prolonged heating increases and the maximum content of chromium which will permit this freedom decreases. It is therefore desirable to increase the nickel content, which is preferably at least 38% The alloys mayalso contain up to 0.6% titanium. Titanium increases the stress-rupture strength of the alloys, and for this purpose they advantageously contain from 0.10% to 0.35% titanium. However, titanium also makes the alloys more susceptible to embrittlement, and in tinum contents must be further correlated with the content of titanium. In fact each 0.1% titanium requires an additional 1% nickel to offset this susceptibility.

The accompanying drawing is a graph in which the nickel content (percent Ni) minus ten times the titanium content (percent Ti) is plotted against the chromium content (percent Cr) and curves marked with aluminum con tents (percent A1) are shown. In the alloys according to the invention the nickel content, chromium content, aluminum content and titanium content are so correlated that the point on the drawing corresponding to [(percent Ni)- l0(percent Ti)] and percent Cr lies in the area ABCDEA and on or to the left of the aluminum-content curve (if any) corresponding to percent A1 or (if there is no such curve) to the next highest percent Al.

It will be seen that the lowermost aluminum-content curve is marked 2.5%. If the aluminum content is 2.5% or less, the nickel and chromium contents must be so correlated that the point corresponding to the alloy is in the area ABCDEA. If percent Al is, for example, 2.55, the point must lie on or to the left of the 2.6% A1 curve.

The required correlation between minimum nickel content, maximum chromium content and aluminum content is set forth in the following Table I:

TABLE I Minimum content of [percent Ni-lflgpezeent Ti)] at indicated chromium con en Percent Al 19% Cr 20% Cr 21% Cr 22% Cr 23% Cr 24% Cr Alloys with less than 19% chromium have relatively poor resistance to sulfidizing and carburizing environments, and at chromium contents greater than 24% the high nickel content required to ensure that the alloy is not susceptible to embrittlement again reduces corrosionresistance. Preferably the chromium content does not exceed 22%, and most advantageously it is from 20.5% to 21.5%.

The alloys become less susceptible to embrittlement as the nickel content increases, and this is why a minimum of 38% nickel is preferred, but with more than 48% nickel their resistance to corrosion is diminished, and preferably the nickel content does not exceed 46%.

Carbon in amounts up to 0.15% improves the stressrupture ductility of the alloys at the expense of some reduction in stress-rupture strength, and more than 0.15% carbon drastically impairs the strength. Preferably the alloys contain from 0.04 to 0.12% carbon.

The alloys may contain other elements in addition to those already discussed. Thus, the stress-rupture strength of the alloys, and to some extent their impact strength, is increased by additions of boron, which may be present in amounts up to 0.2%, e.g. about 0.001% to 0.02%, but preferably not more than 0.005%, e.g. about 0.003% to 0.004% boron.

The resistance of the alloys to oxidation and scaling is improved by additions of rare-earth metals, for example as the mixture known as Mischmetall, or of yttrium, and the alloys may contain up to .3%, e.g. from 0.03 to 0.1% of rare earth metals and/or up to 2%, e.g. from 0.3 to 0.8%, of yttrium.

some of which are examples of the invention and others of which are given by way of comparison. The tests included corrosion test performed by subjecting the alloys for 1000 hours to attack by a gas mixture of hydrogen with 1.5 volume percent of hydrogen sulfide flowing at a rate of 15 litres/hour. The tests also included impact tests performed on the alloys in one of two conditions, resulting from the following treatments:

Condition X: Solution-heated for 2 hours at 1050 C., aircooled, then heated for 1000 hours at 700 C.

Condition Y: Solution-heated for 2 hours at 1050" C., air-cooled, cold-worked to effect reduction, then heated for 1000 hours at 700 C.

TABLE II Corrosion resistance, depth of penetration in Room-temperature in. 10- after Charpy V-notch 1,000-hour impact strength, Composition (weight percent) exposure at It.lbf.

0 Al Gr Ni Tl B 650 0. 800 C. X Y

The balance of the composition, apart from impurities,

Silicon, which may be present as an impurity, while marginally improving resistance to oxidation, scaling and sulfidation, has a marked deleterious effect on impact strength and susceptibility to embrittlement, and should be maintained as low as possible. The silicon content must be below 1% and is preferably below 0.5%, and most advantageously below 0.25%. The other most common impurity is manganese, which may be present up 1% To develop the full stress-rupture strength of the alloys in the wrought form they must be subjected to a solution heat-treatment which may consist of heating for from 30 minutes to 8 hours in the temperature range of 950 C. to 1200 C. and preferably in the range of 1100 C. to 1200 C. If desired the alloys may then be aged, e.g. by heating for from 1 to 24 hours in the temperature range of 600 C. to 900 C. but since ageing will in any event take place during the initial stages of service in this temperature range a special ageing treatment may be omitted. The alloys may be cooled at any convenient rate after each heat-treatment stage.

The improved resistance to embrittlement without loss of resistance to corrosion by hydrogen sulfide/hydrogen atmospheres that is obtained by controlling the composition of nickel-chromium-iron alloys in accordance with the invention is shown by test results on various alloys,

The position of each of the alloys is indicated in the drawing by its letter or number.

The figures of corrosion resistance show little variation as a result of the compositional variations in the alloys.

The embrittlement of the alloys that are not according to the invention is shown by the impact values, particularly in the accelerated test. All tne alloys in accordance with the invention retained impact strengths in excess of 45 ft. lbf. after heating for 1000 hours without coldworking and not less than 30 ft. lbf. even after heating for 1000 hours in the accelerated test, together with satisfactory corrosion-resistance. The importance of the correlation is shown by comparison, for instance, of Alloys X and 9, the former containing too much aluminium in relation to its nickel and chromium contents, and the latter, with somewhat similar nickel and chromium contents but less aluminum, being much more resistant to impact. Alloy U was nearly satisfactory, but did not contain the proper amounts of nickel and chromium for its high aluminum content.

In Table III the stress-rupture properties of six further alloys in accordance with the invention (Nos. 12 to 17) are compared. These results demonstrate the effect of temperature of solution heat-treatment and ageing heattreatment and also the effect of carbon content (Alloys 12 to 14) and titanium content (Alloys 14, 15 and 16) on these properties.

The alloys are particularly suitable for use in the 5. An alloy according to claim 1 wherein the carbon wrought form and may be hot-worked by conventional about methods, e.g. forging, hot-rolling and extrusion, and are An alloy according 9 damn I contammg about f 0.10% to about 0.35% tltamum. readily weldable even under severe condltlons 0 re- An alloy according to claim 1 containing about straint. 0.001% to about 0.02% boron.

TABLE III Stress-rupture properties as 8.5 tont./ln. /700 C. after the following solution and ageing treatments 1 hour, 980 C. 1 hour, 1,150 C.

hr./700 c. 15 hr./850 0. 16 hr./700 C. 15 hit/850 C. Composltlon(weight percent) Lite Elong., Life Elong., Life Elong., Life Elong., Life Elong., Life Elong., Alloy 0 Al Cr Nl Tl B (hr.) percent (hr.) percent (hr.) percent (hr.) percent (hr.) percent (hr.) percent 1 l i 8. An alloy according to claim 1 containing at least one 1. An alloy characterized by resistance to sulfidation metal from the group consisting of about 0.03% to about and carburization and by resistance to embrittlement upon 0.3% rare earth metal and about 0.3% to 2% yttrium. prolonged heating in the temperature range of about 400 C. to about 900 C. and containing, by weight, at least References Cited about 32% to about 48% nickel, about 19% to about UNITED STATES PATENTS 22% chromium, about 2.2% to about 3.5% aluminum, up

to about 0.6% titanium, with the nickel content (percent 2%? 3; a1 2?? Ni), chromium content (percent Cr), aluminum content 2071645 2/1937 5 15} (percent Al) and titanium content (percent Ti) so cor- 9/1956 61 3 X related that the point on the accompanying drawing cor- 2920956 1/1960 g 75 1 responding to [(percent Ni-lO (percent Ti)] and (percent R 242 12/1956 at a Cr) lies in the area ABCDEA and on or to the left of the 2&606113 8/1952 r 1 aluminum-content curve (it any) corresponding to percent 2775536 12/1956 f 1 Al or (if there is no such curve) to the next highest per- 10/1957 1 cent A1, up to about 0.3% of a rare earth metal, up to 3505028 4/1970 "-171 about 2% yttrium, up to about 0.02% boron, up to about out It 75-171 X 0.15% carbon, up to about 0.5% silicon, up to about 1% 40 OTHER REFERENCES manganese, and the balance essentially iron.

2. An alloy according to claim 1 in which the nickel gg ig ggh gg m Corroslon content is from 38% to 46%.

3. An alloy according to claim 1 containing about HENRY w TARRING 1L primary Examiner 20.5% to about 21.5% chromium.

4. An alloy according to claim 1 wherein the carbon U5, ()1, X R,

content is at least about 0.02%. -171 m *1 k N; i W memmeme es eeeeeeiies Patenz No $690,873 Defined September 12. 1672 Inventoflfl) PAUL ISIDORE FONTAINE It is certified that error eppem'e in the weave-identified patent ancl that said Letters Patent are hereby eeteeeteqi as shown belz Col. 4-, line 56, for "tne" read the Col. 6,, Table III, last column under 1 hour 1,15oc.,",

read "0. 5.9, 36A, 1 m, 3@9 and Signed and sealed this 29th day of May 1975.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR. Attesting Officer 

